Block groove above main bearing?

[JonKaase]

Something I'm wondering... Some new blocks are coming with a big groove above the main bearing. I know it's to feed extra oil holes to be drilled in the upper main bearing. But why? In 45 years fo assembling race engines, I've never drilled 1 hole in a main bearing. Even in a big 825" boss hemi, with 3" mains, 8600 RPM and 18 gallons a minute of oil rushing through it, we never drill or enlarge the oil slot in a main bearing. But a new Motorsport Mod motor 5.4 aluminum block comes with a huge groove, about 1/3 of the main surface is taken away with the groove. Now we have an RHS aluminum LS Chevy block, same thing, huge groove. Apparently, whoever thought the groove was a good idea has never played the Chess Game of line honing an aluminum block with steel caps, and 1/3 of the aluminum surface missing. The housing will get real big real fast, going toward the groove, because it cuts so easy there with no surface area.

Does anyone think the groove is important? Jon

[robert1]

I know the Cup guys do this. I don't know why. I have posted in the past about the tooling needed to do this. I guess we'll wait and see if there are any responses (worth looking at). Here's a pic of an old Cup motor I have in the shop. The 2 holes off to the sides are pin oilers. I did an aluminum late model motor like this last year which is why I was looking for the tooling.

[ProPower engines]

It's possible they never ment to have them linehoned. Import blocks are similar and require line boring to correct any mainline issues. Touching up the mianline woule be tricky in this design with no center support in the block below the bearings.
Having not seen one of the RHS blocks do they have the appearance of being bored only or does there appear to be a crosshatch type finnish in the block or caps?

[Lem Evans]

Something I'm wondering... Some new blocks are coming with a big groove above the main bearing. I know it's to feed extra oil holes to be drilled in the upper main bearing. But why? In 45 years fo assembling race engines, I've never drilled 1 hole in a main bearing. Even in a big 825" boss hemi, with 3" mains, 8600 RPM and 18 gallons a minute of oil rushing through it, we never drill or enlarge the oil slot in a main bearing. But a new Motorsport Mod motor 5.4 aluminum block comes with a huge groove, about 1/3 of the main surface is taken away with the groove. Now we have an RHS aluminum LS Chevy block, same thing, huge groove. Apparently, whoever thought the groove was a good idea has never played the Chess Game of line honing an aluminum block with steel caps, and 1/3 of the aluminum surface missing. The housing will get real big real fast, going toward the groove, because it cuts so easy there with no surface area.

Does anyone think the groove is important? Jon

I doubt it. The only one I've had in my hands that were done that way were the old FMS A460 blocks...the ones with the bore set to be honed to 4.6" , valley holes plugged, etc.
I suspect it is an idea whose's time has past.

[Walter R. Malik]

SOME engines do have a problem with oiling the main bearings, (usually those with really tight clearances), and it seems like this is an idea where it has migrated to engines which don't have that problem.

We had a main bearing problem in the early 90's with aluminum small blocks running really tight main clearances, (.0008" to.0012" cold that would open considerably after warm-up), with alcohol injection in sprint cars; doing this, cured the symptoms.

Someone probably put a fix in other blocks and applications where there was no need to have one.

[wyrmrider]

I've done similar on Big block Chryslers and Hemi's, once with a non side oiler ford
feeding the mains from 3 oclock

[ProPower engines]

I recently did an offshore race engine and installed piston cooling jets but kept the groove width to a minimum but in
reality how much load is really on the upper half of the bearing shell anyway? While it completes the 360deg bearing surface
there is not anywhere the load carrying required in the upper half compared to the lower half which is where all the thrust is directed.
As far as I believe there is not real bearing load support lost by doing this except for convenience of diverting oil to extra locations such as pin/piston oiling jets or some other location requiring oil flow.JMO

[jsgarage]

I'm with Wyrmrider on this. We redrill Cleveland and sometimes BBF main oil passages (3 o'clock) to better fill the bearing space. But with the blocks I work on, I've never noticed any reliefs above the bearing to help us do this.
I have drilled a bearing, though- the front upper main in Fontana aluminum race blocks has one oil passage slightly off; you can either slot its oil hole sideways a little, or punch a hole in the insert that falls into the bearing groove. Does it help? Probably not- the block I'm currently working on was the 'factory-sponsored' 410-class sprint engine that ran So-Cal racetracks for 8 years (Danny Pivovaroff's #2 car)- with that oil passage misaligned.

[robert1]

I recently did an offshore race engine and installed piston cooling jets but kept the groove width to a minimum but in
reality how much load is really on the upper half of the bearing shell anyway? While it completes the 360deg bearing surface
there is not anywhere the load carrying required in the upper half compared to the lower half which is where all the thrust is directed.
As far as I believe there is not real bearing load support lost by doing this except for convenience of diverting oil to extra locations such as pin/piston oiling jets or some other location requiring oil flow.JMO

I had a cast iron 350 with splayed caps come in that was cracked through the web at 45° and an aluminum motor that was drilled for the oilers that cracked right down the hole in the web.

[CNC BLOCKS]

I recently did an offshore race engine and installed piston cooling jets but kept the groove width to a minimum but in
reality how much load is really on the upper half of the bearing shell anyway? While it completes the 360deg bearing surface
there is not anywhere the load carrying required in the upper half compared to the lower half which is where all the thrust is directed.
As far as I believe there is not real bearing load support lost by doing this except for convenience of diverting oil to extra locations such as pin/piston oiling jets or some other location requiring oil flow.JMO

I had a cast iron 350 with splayed caps come in that was cracked through the web at 45° and an aluminum motor that was drilled for the oilers that cracked right down the hole in the web.

Had a block from Gibbs racing a few years ago that was cracked through the webbing right where the piston oiler was, The lifter galley was balck from heat so I would say detonation was the major cause of the cracks.

[ProPower engines]

I recently did an offshore race engine and installed piston cooling jets but kept the groove width to a minimum but in
reality how much load is really on the upper half of the bearing shell anyway? While it completes the 360deg bearing surface
there is not anywhere the load carrying required in the upper half compared to the lower half which is where all the thrust is directed.
As far as I believe there is not real bearing load support lost by doing this except for convenience of diverting oil to extra locations such as pin/piston oiling jets or some other location requiring oil flow.JMO

I had a cast iron 350 with splayed caps come in that was cracked through the web at 45° and an aluminum motor that was drilled for the oilers that cracked right down the hole in the web.

But when looking at the bearing itself was it showing signs of damage caused by the grove under the shell?
While all blocks are prone to cracking under the severe stress loads of racing I am looking at the bearing it self.
The cracks that went through the oiler holes just shows it weakened the block in that area.
And if the tune is off detonation will destroy any block. as Carl mentioned the heat generated in the block from detonation will destroy any block but my question is does it affect the bearings ability to do its job with the reduced support under it.

I have been working on some internal plumbing for cooling jets that will not require the drilling of the main webs to prevent
the fatigue related cracks that are prone to developing in this area The plumbing is a PITA to deal with and to aim the jets without interfearing with the rotating components.

[grant6395]

dave,
just out of curiosity,what offshore engine were you working on with piston oilers?sounds pretty serious.anyone around here doesnt play that hard as far as i know..

[robert1]

I recently did an offshore race engine and installed piston cooling jets but kept the groove width to a minimum but in
reality how much load is really on the upper half of the bearing shell anyway? While it completes the 360deg bearing surface
there is not anywhere the load carrying required in the upper half compared to the lower half which is where all the thrust is directed.
As far as I believe there is not real bearing load support lost by doing this except for convenience of diverting oil to extra locations such as pin/piston oiling jets or some other location requiring oil flow.JMO

I had a cast iron 350 with splayed caps come in that was cracked through the web at 45° and an aluminum motor that was drilled for the oilers that cracked right down the hole in the web.

But when looking at the bearing itself was it showing signs of damage caused by the grove under the shell?
While all blocks are prone to cracking under the severe stress loads of racing I am looking at the bearing it self.
The cracks that went through the oiler holes just shows it weakened the block in that area.
And if the tune is off detonation will destroy any block. as Carl mentioned the heat generated in the block from detonation will destroy any block but my question is does it affect the bearings ability to do its job with the reduced support under it.

I have been working on some internal plumbing for cooling jets that will not require the drilling of the main webs to prevent
the fatigue related cracks that are prone to developing in this area The plumbing is a PITA to deal with and to aim the jets without interfearing with the rotating components.

Both of the blocks that cracked did not have the groove. The aluminum block had notches cut to feed the oilers. The blocks with the groove make no marks on the back of the bearings.

[ProPower engines]

dave,
just out of curiosity,what offshore engine were you working on with piston oilers?sounds pretty serious.anyone around here doesnt play that hard as far as i know..

I am doing a 560 inch BBC and a Pro-Charger forced induction system. While I am shooting for around 1000-1100HP it is a max effort engine and in the past the owner had a shop doing work on it but it was short lived between melt downs and bearing failures.
The fellow that owns the boat does race it some but its more of a toy then a full on race boat.
I am just correcting all the previous mistakes that were made as the engine had several repairs and and only would run a short time because of mistakes made.

[Kevin Johnson]

I would guess that it has to do with the effects of register on the oil supply to the rods combined with allowing a greater properly oriented area for acceleration of the boundary layer of oil to journal speed; this might allow lower pressures/volumes to be successfully used (ultimately improving emissions *). The degrees of freedom of the oil movement at a kinetic level are influenced so as to favor concentric distribution and flow rather than a higher inital rate of loss to the margins **. Modeling is probably catching up in ability to accurately represent some of the ideas touched on earlier (Malik at GM circa 1986, for example).

* One of the things that came up in discussing the LS7 issue was the effect of aftermarket valve gear on the Bond size and volume of oil droplets introduced to the crankcase ventilation system. Speedtalk readers probably would care little about this but an OEM is constrained to meet emissions.

** My guess is that rod bearing wear in some BMW V8s is affected by this over long usage but at the rod rather than the main.